Faking depth with rotoscoping

- When you add synthetic elements such as 3D titles to a moving video, it's always a good practice to look for places where you can integrate them better into the scene. For example, place the title between elements so it would look as if it's really there. Fortunately, After Effects has some automatic technology which makes it fast and easy to achieve. So everything is looking quite nice. Let's see it in full screen. Except of this part where the rock is going under the title, and this should be fixed. The rock actually should hide the title. And you can do it very fast and almost completely automatically using the roto brush tool. So in order to achieve it, let's select the source footage and duplicate another copy by pressing, of course, command + D, control + D on the PC. I'm going to remove the 3D camera tracker effect from this one because otherwise it will just make our project size very large on the hard drive. Then I'm going to take it and place it above everything. Now, I just want to find out where exactly I need to create this isolation part. So, I'm going to press T, reduce the opacity to 50%. This way, I can see the title below and then I'm going to dream the end of the layer in this point of time, so three seconds and 14 frames by pressing option and opening bracket, alt will be the same key on the PC. And then let's just move, I guess to almost where the title leaves the screen. So, something like this, maybe few frames after and we'll do the same for the other end so option and the closing bracket to dream the layer and then we can go to the beginning, bring back the opacity to 100% and now, in order to work on this composition, we need to hold down option or alt and double click it. This way, it will open up in the layer source window. Now, I'm going to select the roto brush tool and I want to enlarge the diameter. So, I'm going to hold down command, control on the PC, and drag to the right, and then I'm just going to draw a line over here and maybe also over here. It doesn't really matter because this part is not going to be part of the obscuration that we need to create. It is just for safety make sure that we are including only the necessary parts. Then, I'm going to extend this propagation area until the end of this clip and we can also dream the beginning and then I'm just going to go one frame at a time by pressing page down and see how well After Effects is coping with this automatic matte generation using the roto brush tool. Now, you can also move to full frame so you get a better result, a better idea of how this is going to work. And if you trust the technology you can also press space bar, and this, of course, will create a preview and at the same time we also generate the matte for you. And I'm just making sure that this magenta line is preserved throughout the end of this shot and it looks like After Effects is creating a decent matte since we have enough contrast in this frame. Once it's finished and you are happy with the result, I highly recommend to freeze it, meaning to cache those frames and bake them into the project file and this will save you a lot of time if you are going to reopen this file and play with the position of the 3D titles or anything else that you will modify in the future. So, I'm just going to let it run through the rest of the frames. And once this process is done, you can see a blue bar over here. I'm just going to go out of full frame and also return to the composition view so we can get a sense of how this is working and let's just scrub it to different places and if there is a need, by the way, you can do some post modifications for the matte that you just generated. So you can play with the filler, contrast, you can shift the edge, or you can reduce the chatter. This is always a good idea, so I'm just going to bring it to its full value of 100%, but all the other stuff looks just fine. So, this is how you can use the roto brush automatic effect in order to include or exclude elements from the frame and since we are placing the same clip above the rest, we're actually creating the illusion that this title over here is part of the 3D scene, which means that it is located underneath this rock formation.